function showPic(whichPic){
        let source=whichPic.getAttribute("href")
        //(whichPic指向<a>元素，调用getAttribute得到"href"的参数
        let placeHolder=document.getElementById("placeholder")
        //获取占位图片
        placeHolde.setAttribute("src",source)
        //将获得的href替换掉src，写入js文件
        let text=whichPic.getAttribute("title")
        let description=document.getElementById("description")
        //description.firstChild.nodeValue=text;
        description.innerHTML=text;
        return false;
    }